Method and equipment for reducing the fog arising from humid exhaust air

Abstract: The invention concerns a method and an equipment for reducing the fog arising from humid exhaust air. The air (L₁) that is removed from a room or a building or from a process is cooled, and, here-upon, mixing air (L₂) is mixed with said exhaust air. Hereupon, the partly or fully combined air flow (L₁ + L₂) is passed outdoors.

Description: The invention concerns a method and an equipment for reducing the fog arising from humid exhaust air. Mixing of an exhaust air that is in the saturated state with the outdoor air almost always produces fog. Fog arises when the status point of the air enters into an area in which all the humidity contained in the air cannot be accommodated in the air in the form of water vapour. The amount of fog that is formed can be reduced by cooling the exhaust air. Since the exhaust air still remains in the saturated state, occurrence of fog cannot be prevented. In the solution in accordance with the present invention, cooled exhaust air is mixed with heated outdoor air. This has the effect that the exhaust air is no longer in the saturated state. When the exhaust air is mixed with the outdoor air, the humidity can be accommodated in the mixture in the form of water vapour if a sufficiently large amount of heated outdoor air has been mixed with the exhaust air. In order to enhance the effect of the mixing, the exhaust air is first cooled, in which case a smaller amount of heated outdoor air has to be mixed. The exhaust air is cooled by means of a liquid/air or air/air heat transfer device, and thermal energy obtained from the exhaust air is used favourably for heating the outdoor air to be mixed. The method in accordance with the invention for reducing the fog arising from the humidity contained in exhaust air is defined in by the features of claim 1. DE-C-413 576 discloses mixing of outside air with exhaust air, which is not cooled before mixing. The equipment in accordance with the invention for reducing the fog arising from the humidity contained in the exhaust air is defined by the features of claim 3, the preamble of this claim being based on DE-C-413 576. GB-A-601 023 discloses an apparatus for extracting heat from used air, wherein the air is passed through two heat exchangers. In one of these, heat in the used air is transferred to fresh air. In the following, the invention will be described with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawing, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1A illustrates the mixing of exhaust air and outdoor air in a Mollier diagram in a prior-art solution. Figure 1B illustrates the solution in accordance with the invention. Figure 2 illustrates a solution of equipment in accordance with the invention. Fig. 1A illustrates a case in which outdoor air at -1°C and saturated exhaust air at 45°C are mixed together. The example of Fig. 1A corresponds to mixing of exhaust air and outdoor air in a conventional prior-art solution. Fog is produced in the part of the mixing line placed below the saturation curve, that is in respect of the whole of the mixing from the status point 1 to the status point 2. In Fig. 1B, in accordance with the invention, the mixing of the outdoor air and the exhaust air has been carried out so that the exhaust air has first been cooled from 45°C to 15°C, i.e. by 30°C from the status point 1 to the status point 2. Hereupon, with said air, outdoor air has been mixed which has been heated from the status 3 to the status 4, i.e. to 24°C. In this case, the amount of outdoor air that is mixed is 50 % of the amount of exhaust air, and so the state of the exhaust air that is blown into the open air corresponds to the point 5. Thus, during the mixing from the status point 5 to the status point 3, one does not enter outside the saturation curve, i.e. below the curve as shown in Fig. 1B, so that fog is not produced. Figure 2 illustrates a solution of equipment in accordance with the invention. In the way shown in Fig. 2, the exhaust air is passed through the duct 10 in the way shown by the arrow L 1 out of the building R, out of its interior space H or out of a process in the building. The exhaust air is passed through the duct 10 outdoors U. The duct 10 includes a heat exchanger 11. Thus, the exhaust air L 1 is cooled and heat is recovered from it by means of the heat exchanger 11. The heat exchanger 11 transfers heat to the heat exchanger 12, which may be favourably a plate radiator. By means of the heat exchanger 12, the mixing air L 2 is heated. The heat exchanger 12 is placed in the mixing-air duct 13, and mixing air L 2 is taken from the open air U and transferred by means of the blower P into the mixing unit 14, in which the mixing air L 2 and the exhaust air L 1 are mixed, being removed as partly or fully mixed into the air atmosphere in the open air U. Thus, in the solution in accordance with the invention, the exhaust air L 1 is cooled, and in the mixing unit 14 said exhaust air is mixed with outdoor air that has been heated by means of a heat exchanger, preferably a plate radiator or some other arrangement of equipment, said outdoor air being produced favourably as an amount of about 50 % of the amount of the exhaust air. During mixing, the humidity present in the exhaust air remains in the form of water vapour, and fog is not produced. The mixing air L 2 is heated by means of the thermal energy recovered from the exhaust air.

Claims: Method for reducing the fog arising from humid exhaust air, characterized in that air (L 1 ) that is removed from a room or a building or from a process is cooled and that, hereupon, mixing air (L 2 ) taken from the open air and thereafter heated is mixed with said exhaust air, and that the partly or fully combined air flow (L 1 + L 2 ) is passed outdoors. Method as claimed in claim 1, characterized in that, in the method, the mixing air (L 2 ) is heated by means of thermal energy recovered from the exhaust air (L 1 ). Equipment for reducing the fog arising from humid exhaust air by a method according to claim 1, comprising a duct (10), through which the exhaust air (L 1 ) is passed out of the building (R), from its interior space (H), or from a process, and a mixing-air duct (13), through which mixing air (L 2 ) is passed into a mixer unit (14), in which the exhaust air (L 1 ) and the mixing air (L 2 ) are mixed partly or fully characterized in that the exhaust air duct (10) comprises a heat exchanger (11) for cooling the exhaust air (L 1 ) and the mixing air duct (13) comprises another heat exchanger (12) for heating the mixing air (L 2 ), which is taken from the open air, before mixing in the mixer unit (14), the mix being passed outdoors (U). Equipment as claimed in the preceding claim, characterized in that there is a blower (P), by whose means the air is circulated from outdoors through the heat exchanger (12) into the mixing unit (14). Equipment as claimed in claim 3 or 4, characterized in that the heat that has been recovered from the exhaust air in said heat exchanger (11) is transferred to the mixing air heating heat exchanger (12).

Inventors: KOTAJAERVI JUKKA, LALLI ESKO, KOTAJAERVI, JUKKA, LALLI, ESKO, Kotajärvi, Jukka
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: F24F3
IPC codes: F24F3